1. Field of the Invention
The invention relates to a lens, and more particularly to a zoom lens.
2. Description of the Related Art
A zoom lens differs from a fixed focal length lens in that the focal length of a zoom lens is adjustable within a certain range. When a zoom lens zooms to a telephoto end, the distant object looks closer and magnified. When a zoom lens zooms to a wide-angle end, the field of view is expanded to accommodate a wider range of image. The fixed focal length lens doesn't have zoom in and zoom out function as the zoom lens has, so the current digital still cameras and digital video cameras are mostly equipped with zoom lens.
Zoom lens is developed toward high zoom ratio, smaller F-number and high resolution as higher image quality and a variety of applications are required by users. However, it is not easy to achieve that a zoom lens of a high zoom ratio has smaller F-number and high resolution.